TCP/IP Jennifer Lewis

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Introduction to TCP/IP By definition, TCP/IP is a suite of protocols that allow any system to connect to any other system using any network topology. TCP/IP allows computers of different systems and architectures to communicate with one another without limitations. For example, your Dell PC at home running Windows XP can communicate with an IBM Unix Class Server in Bangalore running AIX UNIX using TCP/IP. Before the advent of the Internet, companies used a hierarchical system for their network communications (see Figure 1). This hierarchical system was a single large system, sometimes called a mainframe, which acted as a “host” in the network. Nodes, either dumb terminals or line printers, would connect to a device called a communications controller, which would act as the intermediary between the host and the nodes. The host would communicate through the communications controller, and the communications controller would relay the messages to the nodes.

The problem with this method is many of these systems used proprietary network architectures and protocols. For example, IBM and DEC, two leading mainframe computer manufacturers, use different architectures and protocols. All the equipment used in this architecture had to be from the same manufacturer. Plus, it was difficult to interact with other networks of different architectures. National defense required a need for sharing computer resources without boundaries. In 1969, ARPANET was created by the United States Defense Advanced Research Project Agency. In order for computer resources to be able to share information without boundaries, TCP/IP was launched in 1973 as a standard form of communication. As illustrated in Figure 2, TCP/IP allowed all devices to be treated as fully functional, self-aware network end-points, capable of communicating with any other device directly, without having to talk to a central host first (Hall, 4).

Figure 1: The Hierarchical Network Architecture, a.k.a. the “mainframe architecture” (Hall, 3) In this illustration, the “dumb terminals” communicate through the communications controller. The communications controller actually communicates with the mainframe, or host, and relays the messages back to the “dumb terminals”.

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Use of TCP/IP How is TCP/IP used today? It is used in two types of communication: Internet communication and Internetwork communication. Internet communication is communication throughout the global network of TCP/IP-based systems. Internetwork communication is communication within the Local Area Network (LAN) or Wide Area Network (WAN). Examples of Internet communication • E-mail – TCP/IP contains protocols to allow a node to send and receive e-mail. • Web browsing – TCP/IP protocols are used to allow a node to use a web browser to

go to a particular web site. • Sending and Receiving files – TCP/IP protocols are used to allow a node to connect

to a machine and either upload (send) files to the machine or download (receive) files from the machine.

Examples of Internetwork communication • Architecture-independent communication – The LAN or WAN does not have to

have the same manufacturers for all the devices, the same architecture, or the same operating systems on each device. By using TCP/IP, machines of different architectures, such as mainframes and personal computers, or machines running different operating systems, such as Windows and Linux, can communicate with one another.

How It Works TCP/IP is actually a software-based suite of protocols that perform different types of communication, such as sending e-mail. Each protocol communicates on a “port”, which is an open line on which the particular traffic communicates. If a machine wants to act as a host, also known as a server, for a particular kind of communication, the server will have a port open that will allow any requests to connect to it. Figure 3 illustrates how client and server communication works in TCP/IP communication.

Figure 2: The Open Network Architecture with TCP/IP, a.k.a. the “anarchical architecture” (Hall, 4)

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TCP/IP Architecture There are three layers in the TCP/IP Architecture model, which is displayed in Figure 4:

Internet The Internet layer is responsible for tracking the addresses of devices on the network, determining how IP datagrams are to be delivered, and sending IP packets from one host

Figure 4: The TCP/IP Architecture Model.

Figure 3: Simple Illustration of how TCP/IP communication works, using web browsing as an example.

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to another across a specific segment (Hall, 10). Example protocols in the TCP/IP suite that operate in the Internet layer is ICMP (Internet Control Message Protocol), which is a protocol for error-reporting, and ARP (Address Resolution Protocol), which is a protocol that builds address mappings whenever address conversion is required (Hall, 18). Transport The Transport layer is where the communication occurs. There are two protocols that are used for communication: TCP and UDP. TCP provides a highly monitored and reliable transport service, while UDP provides a simple transport with no error-correcting or flow-control services (Hall, 10). The terms used when describing TCP and UDP are connection and connectionless protocols. Connection, which is TCP, means that the destination computer has to acknowledge the sending computer before the sending computer can send the message. Connectionless, which is UDP, means that the sending computer can send the message regardless of whether the sending computer received an acknowledgement from the receiving computer or not. Application The application layer provides the end-user applications with access to the data being passed across the transport protocols (Hall, 11). These applications include: Simple Message Transfer Protocol (SMTP), a protocol that sends e-mail; Post Office Protocol 3 (POP3), a protocol that receives e-mail; Hypertext Transfer Protocol (HTTP), a protocol that allows computers to access data stored on a web server; and File Transfer Protocol (FTP), a protocol that allows computers to upload and download files to and from a server. Is TCP/IP For You? If you are setting up a network configuration that requires communication with other networks, such as the Internet, and if your network will encounter growth, then the answer is a resounding YES. TCP/IP is the standard used for network communication because it allows communication with devices, regardless of manufacturer, device type, or operating system.

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References

Hall, Eric (2000). Internet Core Protocols. Sebastopol, CA, USA: O’Reilly and Associates. Webopedia (2005). ARPANET. Retrieved 9 October 2005 from http://www.webopedia.com/TERM/A/ARPANET.html.